A thickener may be used in industrial plants to recover liquid from pulp, which is a mixture of solids and liquid. For example, water used in mineral processing can become mixed in a pulp. The use of a thickener to recover the water from the pulp byproduct can allow the water to be reused in further mineral processing. A thickener can be a large, round, relatively shallow settling tank with a bottom that slopes toward the center. Settling tanks can be 50 meters in diameter, for example, with some as large as 200 meters in diameter. Pulp can enter the thickener through a feed pipe into a feed well in the center of the thickener, where the pulp can then enter the tank. The solids of the pulp can drop to the bottom of the tank where a slowly rotating rake mechanism can move the settled solids toward a central discharge outlet. Overflow liquid that has been separated from the solids can be collected in a peripheral trough and directed to a pipe outlet for recycling.
Additionally, a chemical flocculent can be added to the pulp to increase the settling rate. The flocculent can cause fine solid particles to bind together and settle more quickly. The efficiency of the thickener may rely on the ability of flocculent to contact the particles to allow for this agglomeration. There can be greater chance of agglomeration when the pulp is diluted as much as possible in the feed pipe, at times as low as 10% solids, for example. As such, a diluted feed pipe can allow for a more efficient solid particle surface contact with the flocculent and thus a faster settling rate.